Antonio Faria Neto

This study investigates the composition–property relationship governing the electrochemical behavior and corrosion resistance for Zr–Nb and Zr–Sn alloys with iron (Fe) contents: 300, 400, and 600 ppm (Zr–Nb), and 1100 ppm (Zr–Sn). An integrated experimental approach combining Open Circuit Potential (OCP), Linear Sweep Voltammetry (LSV), Electrochemical Impedance Spectroscopy (EIS), and Electrochemical Noise (ECN), supported by statistical analysis and multiscale time–frequency methods based on discrete wavelet transforms, was employed to evaluate passive film protectiveness and stability. The results reveal a significant and non-linear influence of Fe content on the corrosion behavior of Zr–Nb alloys and modulates the frequency distribution of electrochemical noise, indicating a mechanistic role in repassivation dynamics. Increasing Fe content shifts the wavelet energy distribution from low-frequency to high-frequency coefficients, indicating a transition from steady-state passivation to intermittent repassivation. This transition is accompanied by increased average polarization resistance and reduced corrosion current densities, albeit with greater statistical dispersion. The Zr-Nb alloy with 600 ppm Fe exhibited pronounced electrochemical noise dispersion and intermittent localized transients, highest polarization resistance (~3.1 MΩ·cm2) and highest statistical dispersion (CV > 160%), attributed to passive film rupture followed by rapid repassivation. These results demonstrate that Fe content acts as an electrochemical modifier of passive film stability in zirconium alloys, governing both passive film protectiveness and dynamic stability, emphasizing the relevance of ECN and wavelet analysis for advanced materials qualification.

This study investigates the composition–property relationship governing the electrochemical behavior and corrosion resistance for Zr–Nb and Zr–Sn alloys with iron (Fe) contents: 300, 400, and 600 ppm (Zr–Nb), and 1100 ppm (Zr–Sn). An integrated experimental approach combining Open Circuit Potential (OCP), Linear Sweep Voltammetry (LSV), Electrochemical Impedance Spectroscopy (EIS), and Electrochemical Noise (ECN), supported by statistical analysis and multiscale time–frequency methods based on discrete wavelet transforms, was employed to evaluate passive film protectiveness and stability. The results reveal a significant and non-linear influence of Fe content on the corrosion behavior of Zr–Nb alloys and modulates the frequency distribution of electrochemical noise, indicating a mechanistic role in repassivation dynamics. Increasing Fe content shifts the wavelet energy distribution from low-frequency to high-frequency coefficients, indicating a transition from steady-state passivation to intermittent repassivation. This transition is accompanied by increased average polarization resistance and reduced corrosion current densities, albeit with greater statistical dispersion. The Zr-Nb alloy with 600 ppm Fe exhibited pronounced electrochemical noise dispersion and intermittent localized transients, highest polarization resistance (~3.1 MΩ·cm2) and highest statistical dispersion (CV > 160%), attributed to passive film rupture followed by rapid repassivation. These results demonstrate that corrosion resistance in zirconium alloys for nuclear applications is governed by both passive film protectiveness and dynamic stability, emphasizing the relevance of combined ECN and wavelet analysis for advanced materials qualification.

The growing replacement of metallic alloys by polymer matrix composites in the transport and mobility industries has intensified the need for reliable methods to predict the strength of laminates weakened by fastener holes. As a preliminary step toward the design of composite bolted joints, this work investigates the open-hole (notched) tensile strength of carbon fiber/epoxy laminates using a uniaxial fracture framework based on both the Point Stress Criterion (PSC) and the Average Stress Criterion (ASC) of Whitney and Nuismer. Six balanced carbon/epoxy fabric stacking sequences ranging from [0]₅ to [45]₅ were analyzed for four different hole diameters (3.18, 6.35, 9.52, and 12.70 mm), together with the unnotched reference, totaling 30 evaluated conditions (six different stacking sequences × four different hole diameters and one unnotched laminate). The Konish–Whitney analytical stress distribution was applied to both criteria. The characteristic dimensions d₀ (PSC) and a₀ (ASC) were obtained by fitting reference experimental data. The ASC integral was evaluated numerically over the same stress distribution used for the PSC. A complementary two-dimensional finite-element model with 360-element azimuthal mesh refinement was developed and validated against the classical isotropic infinite-plate solution (K_t ≈ 3), with an accuracy better than 0.1%. Across all 24 (laminate × diameter) combinations, the ASC reduced the root-mean-square prediction error from 15.1% (PSC) to 11.0%, and the mean absolute error from 11.7% to 7.8%. For balanced [0/45] configurations both criteria remained within ±10% of the experimental notched strength, with the ASC narrowing the band to ±3.6%; unidirectional laminates, non-conservative by up to 16% under the PSC, were brought below 7% by the ASC, and ±45°, dominated stacks remained conservative (15–23%), reflecting matrix-driven failure mechanisms outside the scope of either point-wise criterion. Condensed error maps are used to delineate the envelope of applicability of each criterion on the fabric laminate dataset of Soriano and Almeida. The comparative assessment supports the ASC as the more accurate of the two criteria for fiber-controlled configurations within the dataset, while highlighting that any transfer of the calibrated characteristic dimensions to other material systems, geometries, or off-axis-dominated layups would require dedicated validation and, for off-axis stacks, progressive damage modeling.

This study investigates the electrochemical behavior and resistance of zirconium-based alloys in the Zr–Nb and Zr–Sn systems with different iron (Fe) contents: 300, 400, and 600 ppm for Zr–Nb alloys, and 1100 ppm for a Zr–Sn. An integrated experimental approach combining Open Circuit Potential (OCP), Linear Sweep Voltammetry (LSV), Electrochemical Impedance Spectroscopy (EIS), and Electrochemical Noise (ECN), supported by statistical analysis and multiscale time–frequency methods based on discrete wavelet transforms, was employed to evaluate passive film protectiveness and stability. The results reveal a significant and non-linear influence of Fe content on the corrosion behavior of Zr–Nb alloys and modulates the frequency distribution of electrochemical noise, indicating a mechanistic role in repassivation dynamics. Increasing Fe content shifts the wavelet energy distribution from low-frequency to high-frequency coefficients, indicating a transition from steady-state passivation to intermittent repassivation. This transition is accompanied by increased average polarization resistance and reduced corrosion current densities, albeit with greater statistical dispersion. The Zr-Nb alloy with 600 ppm Fe exhibited pronounced electrochemical noise dispersion and intermittent localized transients, attributed to passive film rupture followed by rapid repassivation. These results demonstrate that corrosion resistance in zirconium alloys for nuclear applications is governed by both passive film protectiveness and its dynamic stability, emphasizing the relevance of combined ECN and wavelet analysis for advanced materials qualification.

Power transformers are critical assets for system reliability, as they connect different voltage levels across generation, transmission, and distribution. Their failure can lead to significant impact in multiple aspects such as financial, social, and regulatory. In recent years, rising costs and extended lead times for replacements have posed additional challenges for utilities, increasing the need to extend the service life of the existing fleet. Continuous asset monitoring has emerged as a key enabler of data-driven asset management. By integrating online and offline data along with a comprehensive risk assessment, utilities can better evaluate a transformer fleet, optimize maintenance strategies, and support strategic decisions regarding repair, replacement, or investment in monitoring technologies. This work discusses the parameters used for power transformer condition and risk assessment and presents a framework for a tool designed to support resource allocation and investment prioritization in power transformer fleet asset management.

This study investigates the mechanical behavior of water-washable photosensitive resins used in masked stereolithography (mSLA) 3D printing, evaluating the effect of post-curing time (0, 5, 10, 30, and 60 min) and printing orientation (Flat [XY], Vertical [Z], and On-edge [XZ]) on the material characteristics. Specimens were manufactured according to ISO 527-2 type 1B and ISO 178 standards for tensile and bending tests, respectively. A Matlab algorithm was developed to automate the processing of experimental data. This tool enabled the extraction of parameters to fit distinct mathematical models for the elastic (linear) and nonlinear (polynomial) regimes, allowing the material response to be characterized at different curing times and print orientations. These models were implemented in Ansys Workbench for comparison with experimental results. The results show that increasing the post-curing time from 0 to 60 min raises the elastic modulus from 964.5 to 1892.4 MPa in the Flat [XY] orientation and from 774 to 1661.2 MPa in the Vertical [Z] orientation for tensile testing. In bending testing, the Flat [XY] orientation presented the best mechanical properties, while the Vertical [Z] and On-edge [XZ] orientations showed similar behavior. The numerical simulations adequately reproduced the experimental results, validating the developed constitutive models. Finally, a stress–strain correlation model is presented that enables estimation for any post-curing time between 0 and 60 min. This study provides essential data for optimizing 3D printing processes and developing structural applications with photopolymer resins.

Transformers are critical assets for power system reliability, as they connect different voltage levels across generation, transmission, and distribution. Their failure can lead to significant impacts on multiple aspects. Given the aging transformer fleet, supply chain challenges, and constrained investment capacity, the adoption of risk-based strategies is essential to support long-term maintenance planning and investment. This paper proposes a multicriteria framework to assess the probability and impact of transformer failure, enabling a more comprehensive and data-driven risk evaluation. The method was applied to a sample fleet, enabling the identification and prioritization of the most critical units through a risk plot. The framework enhances asset management by identifying critical units within a transformer fleet, promoting efficiency, reliability, and long-term planning based on objective risk indicators.

The future of the automotive industry appears to hinge on the integration of dissimilar materials, such as aluminum alloys and carbon steel. However, this combination can lead to galvanic corrosion, compromising the structural integrity. In this study, laser-welded joints of 6013-T4 aluminum alloy and DP980 steel were evaluated for their morphology, microhardness, and corrosion resistance. Corrosion resistance was assessed using the electrochemical noise technique over time in 0.1 M Na₂SO₄ and 3.5% NaCl solutions. The wavelet function was applied to remove the DC trend, and energy diagrams were generated to identify the type of corrosive process occurring on the electrodes. Corrosion on the electrodes was also monitored using photomicrographic images. Analysis revealed an aluminum–steel mixture in the melting zone, along with the presence of AlFe, AlFe₃, and AlI₃Fe₄ intermetallic compounds. The highest Vickers microhardness was observed in the heat-affected zone, adjacent to the melt zone, where a martensitic microstructure was identified. The 6013-T4 aluminum alloy demonstrated the highest corrosion resistance in both media. Conversely, the electrochemical noise resistance was similar for the DP980 steel and the weld bead, indicating that the laser welding process does not significantly impact this property. The energy diagrams showed that localized pitting corrosion was the predominant form of corrosion. However, generalized and mixed corrosion were also observed, which corroborated the macroscopic analysis of the electrodes.

Pressure vessels are widely used equipment in several industries, and can operate at high pressure and temperature, which can cause major accidents in the event of a failure. The objective of this work is to analyze the behavior of longitudinal and circumferential stresses at three specific points on the wall of a pressure vessel, two distant points of geometric discontinuity (at the top and side) and one close to geometric discontinuity (at the intersection of the top and the connection) through theoretical, numerical and experimental analyses. The pressure vessel in this work is a piece of equipment used on offshore oil platforms and is part of a natural gas dehydration system. The results showed that the longitudinal and circumferential stresses at the intersection of the top and the connection were higher than the stress values at the top and side for the experimental and numerical analyses, due to the emergence of bending stresses in regions of geometric discontinuity. Another important point was the good correlation of the results between the experimental and numerical analyses using the FEM in the ANSYS software, showing that this methodology is a powerful and reliable tool in the analysis of stresses in pressure vessels.

Este trabalho apresenta uma estação meteorológica inteligente baseada no conceito de Internet das Coisas (IoT), capaz de integrar múltiplos sensores ambientais a uma plataforma de processamento remoto. O sistema foi desenvolvido para apoiar operações aeroespaciais, em especial os lançamentos de Veículos Lançadores de Satélites (VLS), fornecendo em tempo real dados de temperatura, umidade, pressão atmosférica, velocidade do vento, pluviosidade e probabilidade de chuva. As informações são transmitidas para um banco de dados em nuvem (Firebase) e disponibilizadas em uma interface web para consulta imediata. Nos testes realizados, a estação demonstrou confiabilidade, baixo custo e aplicabilidade em operações críticas de meteorologia.